Photodynamic Therapy with A Cationic Functionalized Fullerene Rescues Mice From Fatal Wound Infections

Abstract

Aims: Fullerenes are under intensive study for potential biomedical applications. We have previously reported that a C60 fullerene functionalized with three dimethylpyrrolidinium groups (BF6) is a highly active broad-spectrum antimicrobial photosensitizer in vitro when combined with white-light illumination. We asked whether this high degree of in vitro activity would translate into an in vivo therapeutic effect in two potentially lethal mouse models of infected wounds. Materials & methods: We used stable bioluminescent bacteria and a low light imaging system to follow the progress of the infection noninvasively in real time. An excisional wound on the mouse back was contaminated with one of two bioluminescent Gram-negative species, Proteus mirabilis (2.5 × 10⁷ cells) and Pseudomonas aeruginosa (5 × 10⁶ cells). A solution of BF6 was placed into the wound followed by delivery of up to 180 J/cm² of broadband white light (400–700 nm). Results: In both cases there was a light-dose-dependent reduction of bioluminescence from the wound not observed in control groups (light alone or BF6 alone). Fullerene-mediated photodynamic therapy of mice infected with P. mirabilis led to 82% survival compared with 8% survival without treatment (p < 0.001). Photodynamic therapy of mice infected with highly virulent P. aeruginosa did not lead to survival, but when photodynamic therapy was combined with a suboptimal dose of the antibiotic tobramycin (6 mg/kg for 1 day) there was a synergistic therapeutic effect with a survival of 60% compared with a survival of 20% with tobramycin alone (p < 0.01). Conclusion: These data suggest that cationic fullerenes have clinical potential as an antimicrobial photosensitizer for superficial infections where red light is not needed to penetrate tissue.

Keywords::

• antimicrobial photodynamic therapy
• buckminsterfullerene
• mouse model
• Proteus mirabilis
• Pseudomonas aeruginosa
• wound infection

Financial & competing interests disclosure

At the time of writing, Tim Wharton and Ashlee Jahnke were employees of Lynntech Inc. Lynntech Inc. has licensed a patent on which Tim Wharton and Michael R Hamblin are inventors. This work was supported by the NIH (grants R43AI68400 to Lynntech Inc and R01AI050875 to Michael R Hamblin) and by the US Air Force Medical Free Electron Laser Program (FA9550-04-1-0079). Tianhong Dai was supported by the Bullock Wellman Postdoctoral Fellowship. George P Tegos was partly supported by a Massachusetts Technology Transfer Center Award. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript.

Ethical conduct of research

The authors state that they have obtained appropriate institutional review board approval or have followed the principles outlined in the Declaration of Helsinki for all human or animal experimental investigations. In addition, for investigations involving human subjects, informed consent has been obtained from the participants involved.

Additional information

Funding

At the time of writing, Tim Wharton and Ashlee Jahnke were employees of Lynntech Inc. Lynntech Inc. has licensed a patent on which Tim Wharton and Michael R Hamblin are inventors. This work was supported by the NIH (grants R43AI68400 to Lynntech Inc and R01AI050875 to Michael R Hamblin) and by the US Air Force Medical Free Electron Laser Program (FA9550-04-1-0079). Tianhong Dai was supported by the Bullock Wellman Postdoctoral Fellowship. George P Tegos was partly supported by a Massachusetts Technology Transfer Center Award. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed. No writing assistance was utilized in the production of this manuscript.